An engine may operate during conditions when engine load and speed change with vehicle operating conditions. For example, engine load may change in response to a human driver applying or releasing an accelerator pedal. Engine speed may change when a transmission shifts from a first gear to a second gear. If the engine is operating with advanced spark timing that is near minimum spark advance for best torque or with engine knock limited spark timing, the engine may enter detonation conditions and knock when engine speed and/or engine load change. The engine may knock when end gases in the engine cylinder ignite before they are ignited by a flame front of a spark that is produced via a spark plug. Ignition of the end gases may result in high frequency pressure changes that may cause the engine block to vibrate, thereby inducing an engine knocking sound. In addition, higher pressures resulting from ignition of the end gases may result piston degradation.
The propensity of an engine to knock may increase when the engine is operated under transient conditions because rapid changes in engine speed and engine load may induce fueling or spark timing errors that may increase the propensity for engine knock. Therefore, it may be desirable to reliably detect engine knock during transient engine operating conditions. However, engine knock background noise levels that are based on steady-state (e.g. conditions where engine speed and engine load change less than fifteen percent of their average values) conditions and that are applied to determine the presence or absence of engine knock may be less reliable during transient engine operating conditions. Consequently, it may be difficult to make an accurate assessment of the presence or absence of engine knock during transient engine operating conditions.
The inventors herein have developed an engine operating method, comprising: assessing an engine for knock via a controller according to a total engine knock background noise level that includes individual contributions (e.g., individual amount values) for steady-state and transient base engine knock background noise levels; and adjusting engine operation according to the assessment.
By including adjustments for transient engine knock background noise levels in a total engine knock background noise level, it may be possible to provide the technical result of improving engine knock detection during transient engine operating conditions where engine noise may increase as a function of acceleration of the engine's valve train and secondary acceleration (e.g., Coriolis acceleration) of the engine's valve train. In particular, the engine knock background noise level accuracy may be improved so that detection of engine knock may be improved. A total engine knock background noise level for each engine cylinder may be established, and the total engine knock background noise level may include individual and unique values representing steady-state and transient condition noise levels.
The present description may provide several advantages. In particular, the approach may improve detection of engine knock during transient engine operating conditions. Further, the approach provides for adjusting a total engine knock background noise level for both transient and steady-state engine operating conditions. Further still, the approach may be applicable to variable displacement engines and engines that are not variable displacement engines.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.